The use of thermal recording is expanding in the fields of facsimile telegraphs and printers, labels including POS, etc. This is because thermal recording has the following advantages: (1) development is unnecessary, (2) the quality of paper supports for thermal recording is similar to that of general paper, (3) handling is easy, (4) developed-color densities are high, (5) the recording apparatus is simple and inexpensive, and (6) the recording operation is quiet. Because of the increasing number of applications, the performance requirements of heat-sensitive recording materials have become diverse. A heat-sensitive recording material capable of multicolor recording and a transparent heat-sensitive recording material for overhead projectors have been developed as described, for example, in JP-A-63-265682. (The term "JP-A" as used herein means an "unexamined published Japanese patent application.")
With the recent trend toward the use of electronic medical equipment such as ultrasonic scanners, CT scanners, and X-ray apparatus, a transparent heat-sensitive recording material has also been developed for directly recording images from digital signals that are received from this type of equipment.
However, conventional heat-sensitive recording materials comprising a transparent support and a heat-sensitive recording layer formed thereon are disadvantageous in that image density unevenness in thermal-head recording caused by, e.g., fluctuation in thermal-head resistivity, surface roughness of a glazing layer, and fluctuation in the moving speed of the thermal head or recording material, tends to be more noticeable. This is because the recorded images are observed with transmitted light. A second disadvantage is that conventional heat-sensitive recording materials are subject to density fluctuations with changes in temperature and humidity. Density fluctuations are troublesome in those applications where high image precision is required such as in medical images.